Creating constantly and quickly repeating pulses of particulate material suspended in a carrier means such as air has been a long lasting desire for many applications, in particular for pulses which are well controlled with regard to their shape, to their frequency, and to the amount of material transferred during these pulses. A particularly useful application is during the manufacture of disposable absorbent articles, such as baby diapers, adult incontinence or feminine hygiene pads, and the like, where the manufacturing aims at high production speed and low variability.
In U.S. Pat. No. 4,800,102 (Takada), an apparatus and method for spraying or scattering solid particulate powders onto a substrate is described. The powder is scattered onto a rotatable disc member, which has at least one opening through which a portion of the powder can pass through to reach an underlying substrate, while the non-passing powder is recycled to the powder feeder. Another masking process is described in PCT publication WO-A-92/19198 (Perneborn). Thereby, a device for depositing particles on a moving web of material has an apertured belt which moves over a material web and has a particle dispenser to dispense particles in a uniform pattern in the shape of the apertures of the belt. The particles not dispensed through the apertures are recycled back to the particle feeder.
Both of these systems use the gravity for accelerating the powder particles, and are limited in pulse frequency and hence overall production speed. Further, as part of the powder delivered to the device is recycled, there is only limited control of the amount of powder disposed on the substrate, and hence in the produced article.
U.S. Pat. No. 5,213,817 (Pelley) describes a powder spray ejector oscillating over a flow separator, which separates a portion of the powder being deposited on a web, and the other portion being recycled.
Other approaches use pulsing of an air stream to create a pulsed particle stream, such as described in U.S. Pat. No. 4,927,346 (Kaiser), U.S. Pat. No. 6,033,199 (Vonderhaar). In U.S. Pat. No. 5,028,224 (Pieper) an apparatus and process for providing a pulsed particle stream is described, wherein a continuous gas entrained stream of particles is centrifugally diverted into an accumulation region, from where it is selectively discharged, such as by the use of a pulsed air stream.
U.S. Pat. No. 4,543,274 (Mulder) discloses a powder spray gun wherein high velocity air is said to impact powder entrained air contained in the bore of the gun. U.S. Pat. No. 4,600,603 (Mulder) discloses a powder spray gun apparatus wherein an inverted flow amplifier is located adjacent to the inlet of the gun to enhance blending of powder within the gun. From the inverted flow amplifier, the blended powder is supplied to a downstream air flow amplifier which is operable to impact air entrained powder with a high velocity stream of compressed air. A powder control system controls powder supply from powder supply pumps to the spray gun. The powder pumps are said to be conventional venturi powder pumps.
U.S. Pat. No. 4,770,344 (Kaiser) discloses a powder spraying system including a volumetric or gravimetric material feeding device for metering a quantity of powder into a manifold, and air flow amplifiers connected to passageways formed in the manifold. Kaiser '344 teaches that a problem associated with venturi powder pumps is the difficulty in obtaining a consistently accurate feed rate of powder material, especially when a spray gun is operated intermittently. U.S. Pat. No. 4,927,346 and U.S. Pat. No. 5,017,324 (Kaiser) disclose additional embodiments for depositing particulate material into a pad with a spray gun, including an embodiment having an inverted flow amplifier and an embodiment having a rotating screw for providing a metered quantity of absorbent particles. U.S. Pat. No. 5,037,247 (Kaiser) discloses a powder pumping apparatus having a venturi passageway and an air ejector including a valve mechanism. Kaiser '247 teaches that it is desirable to include a valve in the air ejector to eliminate the “dead zone” in the air supply tube extending between the valve and the inlet to the pump body, and thereby eliminate the powder pulse “tailing effect” experienced in other powder pump designs. However, such an arrangement has the disadvantage of a requiring a valve assembly adjacent to or within the ejector, which may not be practical or even possible in every installation due to space or geometry constraints. These approaches have in common, that they primarily create a pulsed gas/air stream, which accelerates the particles to create a pulsed particle stream. However, such air pulses are difficult to control in stable manner, in particular for higher pulse frequencies and higher particle flow rates.
Henceforth, the present invention aims at overcoming limitations of the known systems, in particular with regard to pulse frequency so as to allow for higher production speeds, as well as with regard to higher throughput on a per pad basis, so as to satisfy the requirements of modern absorbent article design.
As a further objective the invention provides a kit or pack of individual absorbent articles in a cost effective manner.